The phytotoxin Thaxtomin A is the primary virulence determinant for scab disease of beet, carrot, and radish caused by streptomyces scabiei

Authors: Clarke, Christopher; Kramer, Charles; KOTHKA, RAGHAVENDHAR - Oak Ridge Institute For Science And Education (ORISE); Luthria, Devanand - Dave

Submitted to: American Phytopathological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2022
Publication Date: 6/11/2022
Citation: Clarke, C.R., Kramer, C.G., Kothka, R., Luthria, D.L. 2022. The phytotoxin Thaxtomin A is the primary virulence determinant for scab disease of beet, carrot, and radish caused by streptomyces scabiei. American Phytopathological Society. https://doi.org/10.1094/PHYTO-03-22-0072-R.
DOI: https://doi.org/10.1094/PHYTO-03-22-0072-R

Interpretive Summary: Common scab is a major disease of potato caused by Streptomyces bacteria that produce the plant toxin Thaxtomin A. Plant pathogenic Streptomyces can also cause scab diseases on other root crops such as carrot, turnip, radish, and beet. In this work, we tested and affirmed the hypothesis that Thaxtomin A is also required for Streptomyces to cause scab disease on these other crops. Management of scab diseases remains a challenging problem but several disease management tools for potato are under investigation with some promise. Because there is substantial overlap between potato and the tested taproot crops for the causative organisms and mechanisms which cause scab disease, our results will aid scientists in evaluating efficacy of management tools developed for potato on these taproot crops. Alternatively, any management tools developed against common scab for root crops should also be tested for efficacy in managing common scab of potato.

Technical Abstract: Several species of Streptomyces cause common scab, a major disease of potato, primarily through the phytotoxic effects of the phytotoxin Thaxtomin A. Several phytopathogenic Streptomyces species have also been implicated as the causative agents of scab diseases of taproot crops including beet, carrot, radish, parsnip, and turnip. But the molecular mechanisms employed by Streptomyces to infect these host crops is unknown. In this work, we tested the hypothesis that Thaxtomin A biosynthesis is also necessary for Streptomyces-caused scab of beet, carrot, radish, and turnip. Purified Thaxtomin A induced plant stunting and cell death of all four of these species. Streptomyces mutants in which the transcriptional regulator of Thaxtomin A biosynthesis is disrupted were non-virulent on all four crops, and complementation of the transcriptional regulator rescued Thaxtomin A biosynthesis and plant pathogenicity. These results demonstrate that Thaxtomin A is the primary virulence determinant of scab disease of these other crops.